I didn't really follow a HOWTO on it. The easiest way to learn is to just set it up (from Fantastico), login as admin, and mess around with it to your heart's content. Don't worry about all the server config stuff for now, just get the hang of adding articles, news, sections, FAQs, links, etc. Trust me it's easy once you get used to it. I know both Joomla and Postnuke very well (Joomla seems to be faster) so if I were you I'd use Joomla.